which cpu ??

[pcman]

i got mercury km400m-l with 512mb ram and 1.6 (slow) duron but bit confused what cpu to fit. The manual says fits any 462 cpu,on cover it says 333 fsb and inside it says via chipset km400a fsb 200mhz ddr 200mhz, km400 166mhz ddr 166mhz. does this mean bus speed dependant on ddr speed, i was hoping to fit athlon xp heard sempron is slower just confused which cpu to buy.